Erythrocytes – Blood Cells

Blood (Latin: sanguis, Greek: haima) is a suspension of cells in a saline solution containing protein. It makes up 6-8 % of the total body weight and has a pH value of 7.4. The blood carries out many essential functions and is the pivotal point of the whole organism. The following article provides, at a glance, the most important facts about this vital body fluid called blood.

00:01
Hello in the second lecture in our series
on haematology we're going to look at thephysiology and function of some of the major
blood cells, and the learning outcomes thatwe'll be getting from this lecture are as follows:
We will look at red cell production and howthat's regulated by erythropoietin, and we
will explore how red cells contain haemoglobinand how that helps them to carry oxygen to
tissue.
00:29
We will look at the subsets of white cells which
play specific roles in protection against infectionand we will explore how lymphocytes mediate the
function of the immune systemand find out how neutrophils are critical in the
first line of defence against bacteria and fungi.
00:48
In this lecture we are not going to focus
on platelets because they're the subject ofa later lecture on blood clotting.
00:57
Let's look at red cells in a little bit more detail,
by far the most common cell within the blood.
01:07
Red blood cells derive of course from a nucleated
cell within the bone marrowand the first cell that is committed to forming
red cells is the erythroblastand there are rare forms of leukaemia in fact
derived from these cells.
01:23
Red cells are packed with haemoglobin
and they carry oxygen to tissue.
01:29
The reason that we've evolved red cells is that it
allows haemoglobin to be packaged effectivelywithin these blood cells rather than being
free within the blood,the major production of red cells is through this
hormone called erythropoietin and we'll explorethe regulation of erythropoietin in some detail.
01:52
On the right, you'll see a lovely scanning
electron micrograph of red cells and you'll seethat classic biconcave disc structure of the red
cell which allows it to be flexible and flowthrough the capillaries as well as diffusing
oxygen into tissue.
02:14
Now, haematologists can't stop making blood films
and there you’ll see a blood film on the rightand you'll see how red cells look down the
microscope and you'll see the characteristic palecentre because of their shape.
They are around seven microns in diameterand highly flexible structures with the biconcave
shape.
02:39
Now, some red cells in the blood are very young,
because they've just come out of the bone marrowand we call those reticulocytes.
They carry a lot of RNA and that RNA gradually getsdegraded over 2-3 days and the final red cell
then becomes apparent.
03:02
So you'll see on the left reticulocytes can live
for two or three days normally within the blood.
03:07
Around 2% of the red cells are reticulocytes
and we can detect them by staining what we callthe supravital staining with this wonderful dye
called brilliant cresyl blue and you'll seeon the right those cells with the intense blue
stain, those are reticulocytes.
03:28
There's an awful lot in that picture and many
more of them we'd find in your own blood I'm sure.
03:34
Now as well as being physiologically important,
reticulocytes are important clinically becausethey can give us a guide as to the type of anaemia
that we may be dealing with in a patient.
03:46
Because if the reticulocyte count has increased,
it shows that the patient's bone marrow isvery active and pouring out a lot of red cells into
the blood, whereas if we can't find many reticulocytes,it means that there's a problem with the production
of red cells from the bone marrow.
04:05
So when we discuss anaemia in later lectures,
you can see why the reticulocyte count is avery useful test for trying to understand
the etiology of the anaemia.
04:18
Now, the production of red cells is described
by the term erythropeoisis.
04:26
And again, it's represented by those green cells.
04:30
Erythroblasts are the first precursors and
those differentiate into normoblast.
04:38
Normoblasts have a nucleus but then as they
themselves differentiate, the nucleus is ejectedand at that stage, the reticulocytes can be
released into the blood.
04:50
Now we don't know why the nucleus is ejected in
red cell production but it may be that that allowsmore room for haemoglobin production and that
has been selected during evolution as a veryeffective way to increase oxygen transport
within the blood.
05:12
Now the regulation of this process of haemopoiesis
is really controlled through this proteincalled erythropoietin or EPO.
This hormone EPO is produced largely from the kidney.
05:29
Again very surprising finding, the kidney should
be regulating our blood production.
05:36
But if cells in the kidney detect that the blood
is hypoxic in any way, they will then releaseerythropoietin into the blood.
Erythropoietin circulates to the bone marrowand it stimulates the production of red cells.
As you could probably imagine, EPO or erythropoietinlevels are increased in people who are short of oxygen.
For instance, those who live at high altitudeor patients who have lung disease or perhaps, smoke.
You'll see on the right there, a representation ofstimuli to hypoxia, factors such as anaemia,
or low atmospheric oxygen tension.
06:22
That hypoxia is detected by the kidney and
erythropoietin is produced.
06:31
Erythropoietin stimulates haemopoiesis through a
number of mechanisms.
06:35
It increases the differentiation pathway through
erythropoiesis to make more erythropoietic cells.
06:43
It accelerates cell division and it accelerates
release of cells into the blood.
06:51
That can usually address the hypoxia.
Of course, the negative feedback loop is established.
06:59
Erythropoietin is actually a very useful molecule
for clinical therapy and we can use it to stimulatehaemopoiesis in patients with some forms of anaemia.

About the Lecture

The lecture Erythrocytes – Blood Cells by Paul Moss, PhD is from the course Hematology: Basics.

Included Quiz Questions

Which one of these is MOST ACCURATE statement regarding reticulocytes?

They are useful in determining the relative activity of erythropoiesis in the marrow.

They contain a nucleus that is lost soon after release into blood.

Increased presence of reticulocytes indicates anaemia.

They are detected by red stain on supravital staining.

They exist for around 10 days before maturing to erythrocytes.

What is the average size of a normal RBC?

7-8 microns

10 -12 microns

4-5 microns

13-14 microns

15-18 microns

Which of the following stains are used for detection of reticulocytes in peripheral blood smear?

Supravital stain

Leishman stain

Romanowsky stains

Giemsa stain

Myeloperoxidase stain

What is considered an increase in the percentage of reticulocytes in an adult?

>2%

>1%

>0.5%

>0.8%

>1.5%

Which of the following is NOT the function of the erythropoietin in erythropoiesis?

Erythropoietin increases the oxygen-carrying capacity of the RBC.

Erythropoietin increases the erythrocyte production.

Erythropoietin increases the conversion of the stem cells to erythrocytes.

Erythropoietin increases the proliferation and differentiation of progenitors.

Erythropoietin decreases the cell cycle time.

Which of the following scenarios is NOT associated with an increase in erythropoietin levels in the body?

Chronic smoker

Person who is high altitude

Patients with renal cell carcinoma

Patients with exogenous sources of erythropoietin

patients with viral-induced polycythemia

Author of lecture Erythrocytes – Blood Cells

Paul Moss, PhD

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